In recent years there has been considerable interest in intravenous delivery pumps, particularly for the feeding of saline solutions, and the like, to a patient. For many years such materials were fed to a patient only by the force of gravity, which necessitated placing the container containing the liquid for delivery to the patient at a considerable elevation above the patient. These devices were not entirely satisfactory in view of the height requirement and the difficulty in accurately regulating their flow. Regulation of flow could only be secured by counting drops of fluid in a predetermined period of time and then requiring periodical checking by a nurse. Furthermore, it was difficult to maintain a regulated flow over a prolonged period of time. Therefore, in recent years there has been a trend toward developing a positive acting pump which could be accurate in its delivery of intravenous feeding material to the patient, could be readily adjusted and would be positive in its operation, without requiring the placing of the bottle containing the liquid at some distance above the patient. The difficulty with these pumps has been, for the most part, that they were subject to slight variations in the quantity of material delivered, so that absolute accuracy was still impossible. They also have the disadvantage that they were rather expensive and could not be used once and then thrown away, and they were difficult to disassemble, sterilize, and re-assemble, so that sterilization and the maintenance of sterile conditions was difficult. One of the causes of inaccuracy in pumping was the shape of the chamber in which the pumping operation took place. If this is square or cylindrical in shape and is made of light plastic material, the exertion of a pumping force to the material within the chamber causes flexing of the chamber walls and therefore introduces inaccuracies. Many of these pumps used float valves, most of which were cylindrical in shape, and again the force applied to the liquid within the pumping chamber caused flexing of the top and bottom of the cylindrical float. Some of the pumps heretofore suggested have utilized a piston moving into and out of the pumping chamber to apply the pumping force to the liquid within the chamber and this introduced the possibility of leakage and, more important, the possibility of septic materials coming from outside the pump through the wall in which the piston operates and into the material in the chamber. Such a construction involved a rubbing contact between the piston and the wall of the pumping chamber, which produces wear and eventual leakage, and prevented their use for pumping blood.
These disadvantages have been removed in the present invention in which the pump is preferably made of light plastic material, so that it can be made in a few simple moldings and therefore is so inexpensive that it can be thrown away with each use. The pumping chamber is preferably spherical in shape so that the application of pressure to the liquid therein is equal in all directions and cannot deform spherical walls. I use, preferably, a particular form of float valve in which a spherical float is mounted on one end of a lever arm, the other end of which is pivoted to the walls of the respective chambers, which arm carries at an intermediate point a gasket aligned with the inlet into the respective chambers. The gasket preferably is located substantially closer to the pivot point than to the center of the spherical float, thereby giving the float increased force against the inlet due to the multiplication of force through the lever action. The pumping member is a piston enclosed in a tight fitting sheath which is preferably shaped to prevent the entrance of air between the sheath and the piston and is shaped so that the stretching of the sheath occurs in the cylindrical walls thereof rather than at the end, so that there is considerable force applied to the sheath against the piston to return it to its normal, inoperative position. Movement of the piston can be from any suitable prime mover, such as a small motor rocking a lever against the outer end of the piston. Further, the preferred form of pump shown and described permits it to be used as a positive acting and highly accurate pump when it is placed in one position, and can also be used in gravity feed by merely turning the pump upside-down. Thus, the device of the present invention can be used as a pump or in connection with gravity feed without removing it from the feed line, as conditions may warrant.